Summary. In a prospective randomized study, 36 patients with spontaneous rupture of the membranes of ≥4 h duration were stimulated with 3 mg vaginal prostaglandin E2 pessaries or intravenous oxytocin. Oxytocin stimulation was associated with shorter labours and a lower incidence of abnormal cervimetric progress. Of the patients given prostaglandin pessaries, 40% required a second dose after 4 h for slow progress; 45% of the primigravidae subsequently developed abnormal labour which was corrected by augmentation with oxytocin in all cases. One caesarean section was carried out for disproportion, and the remaining 35 patients were delivered vaginally. Prostaglandin pessaries were not associated with an increased incidence of hyperstimulation or sepsis. In conclusion, although PGE2 pessaries are safe in spontaneous rupture of the membranes, intravenous oxytocin is more efficient in stimulating labour.